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Cesarean Risk and Labor Duration in Obese Mothers

Am Fam Physician. 2004 Dec 15;70(12):2369-2370.

The incidence of several adverse outcomes of pregnancy is increased in obese mothers. Most studies have focused on the incidence of cesarean deliveries. Nuthalapaty and colleagues studied other adverse outcomes in mothers undergoing induction of labor.

They studied women with singleton vertex pregnancies of at least 36 weeks’ gestation in a university teaching hospital. Participants had to have an indication for induction but no evidence of chorioamnionitis or cervical dilation greater than 2 cm. Mothers with previous cesarean deliveries were excluded from the study. Extra-amniotic saline was used to ripen the cervix in women with intact membranes. All participants received intravenous oxytocin following the same protocol (i.e., initiation at 2 mU per minute, followed by 2 to 5 mU per minute every 15 minutes over two hours up to 30 mU per minute or until labor progressed). Amniotomy was performed if membranes did not rupture within 24 hours. If the fetal heart rate pattern was reassuring, cesarean delivery was not permitted in nonprogressing women until oxytocin had been administered for at least 12 hours after membrane rupture. Extensive demographic and medical data were collected from the 509 participants.

The overall cesarean delivery rate was 20 percent; the average weight of the 104 women who had cesarean deliveries (97 kg [213 lb, 6 oz]) was significantly greater than that of the 405 women who delivered vaginally (87 kg [191 lb, 6 oz]). The nulliparous women in the highest weight quartile had a 2.5-fold greater rate of cesarean delivery than those in the lowest quartile. In nulliparous mothers, the odds of cesarean delivery increased by 25 percent for each 10-kg (22-lb) increase in maternal weight.

The association between weight and cesarean delivery did not reach statistical significance in parous mothers. Nulliparous mothers in the highest weight quartile had significantly slower rates of cervical dilation compared with mothers in the lowest quartile. They also had a significantly greater time from initiation of oxytocin to delivery. The mean time was five hours longer in this group than in the lowest weight quartile. After adjustment for maternal age, infant birth weight, initial cervical dilation, and diabetes in nulliparous mothers, the risk of cesarean delivery, slowed cervical dilation, and increased duration of labor was found to be associated with increased maternal weight.

The authors conclude that the risk of cesarean delivery is strongly associated with increased maternal weight in nulliparous mothers, and that maternal weight is associated with decreased rate of cervical dilation and increased duration of labor in all mothers.